Haemophilus influenzae is the cause of several serious human diseases, such as meningitis, epiglottitis, septicemia and otitis media. There are six serotypes of H. influenzae, designated a to f, that are identified by their capsular polysaccharide. H. influenzae type b (Hib) was a major cause of bacterial meningitis until the introduction of several Hib conjugate vaccines in the 1980' s (ref. 1. Throughout this application, various references are referred to in parenthesis to more fully describe the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosures of these references are hereby incorporated by reference into the present disclosure). Vaccines based upon H. influenzae type b capsular polysaccharide conjugated to diphtheria toxoid (ref. 2), tetanus toxoid (ref. 3 and U.S. Pat. No. 4,496,538), or Neisseria meningitidis outer membrane protein (ref. 4) have been effective in reducing H. influenzae type b-induced meningitis. The other serotypes of H. influenzae are associated with invasive disease at low frequencies, although there appears to be an increase in the incidence in disease caused by these strains as the incidence of Hib disease declines (ref. 5; ref. 6). Non-encapsulated or non-typeable H. influenzae (NTHi) are also responsible for a wide range of human diseases including otitis media, epiglottitis, pneumonia, and tracheobronchitis. The incidence of NTHi-induced disease has not been affected by the introduction of the Hib vaccines (ref. 7).
Otitis media is the most common illness of early childhood, with 60 to 70% of all children, of less than 2 years of age, experiencing between one and three ear infections (ref. 8). Chronic otitis media is responsible for hearing, speech and cognitive impairments in children. H. influenzae infections account for about 30% of the cases of acute otitis media and about 60% of chronic otitis media. In the United States alone, treatment of otitis media costs between 1 and 2 billion dollars per year for antibiotics and surgical procedures such as tonsillectomies, adenoidectomies and insertion of tympanostomy tubes. It is estimated that an additional $30 billion is spent per annum on adjunct therapies, such as speech therapy and special education classes. Furthermore, many of the causative organisms of otitis media are becoming resistant to antibiotic treatment. An effective prophylactic vaccine against otitis media is thus desirable.
During natural infection by NTHi, surface-exposed outer membrane proteins that stimulate an antibody response are potentially important targets for bactericidal and/or protective antibodies and, therefore, potential vaccine candidates. A family of high molecular weight proteins (HMW1 and HMW2) that are important in attachment of NTHi to epithelial cells has been identified in about 70 to 75% of NTHi strains (ref. 9; ref. 10). These high molecular weight adhesins have been shown to afford some protection in the chinchilla model of otitis media (ref. 11). A second family of high molecular weight adhesion proteins has been identified in about 25% of NTHi and in encapsulated H. influenzae strains (ref. 12; ref. 13, ref. 14). The NTHi member of this second family is termed Haemophilus influenzae adhesin or Hia and the homologous protein found in encapsulated strains is termed Haemophilus influenzae surface fibril protein or Hsf. The hia gene was originally cloned from an expression library using convalescent sera from an otitis media patient, which indicates that it is an important immunogen during disease. The prototype Hia and Hsf proteins demonstrate about 82% sequence similarity, although the Hsf protein is considerably larger. The proteins are comprised of conserved amino and carboxy termini and several repeat motifs, with Hsf containing more repeat sequences than Hia. A high molecular weight protein (200 kDa) has also been identified from Moraxella catarrhalis that has some sequence homology with the Hsf and Hia proteins (U.S. Pat. No. 5,808,024).
Since Hia or Hsf is conserved amongst encapsulated strains of Haemophilus influenzae and about 20 to 25% of non-encapsulated strains, and has been demonstrated to be an adhesin, the protein has utility in diagnosis of and vaccination against disease caused by H. influenzae or other bacterial pathogens that produce Hia or a protein capable of raising antibodies specifically reactive with Hia.
A disadvantage of Hia for use as an antigen in diagnosis, for the generation of anti-Hia antibodies useful in diagnosis and as an immunogen in vaccination is the low recovery of the native protein from Haemophilus influenzae species.
It would be advantageous to provide recombinant Hia protein for use as antigens, in immunogenic preparations including vaccines, carriers for other immunogens and in the generation of diagnostic reagents.